The present invention relates generally to methods and apparatus for determining a person""s visual characteristics, and more particularly to apparatus for determining the refraction of the eye.
Phoropters are apparatus used by optometrists to determine a patient""s visual characteristics, so that proper eye diagnoses can be made and eyewear can be prescribed. In conventional phoropters, a patient looks through the phoropter, in which various test lenses are disposed, at a target eye chart, referred to as a xe2x80x9cSnellen chartxe2x80x9d, while an optometrist moves the test corrective lenses into the patient""s field of view. In some applications, the target may be positioned at a predetermined distance from the patient. The patient is then asked to verbally compare the quality of the perceived image as afforded by one lens versus the prior lens presented. The optometrist takes note of either an improvement or a deterioration in the patient""s vision through such lenses. Systematically, the test progresses towards the xe2x80x9cbestxe2x80x9d test lens entirely based on the patient""s responses. The lens parameters are then used as the basis for a prescription for eyewear.
Unfortunately, as recognized herein the patient can become fatigued during the process and/or misjudge the vision afforded by the various lenses. This can lead to the selection of a less than optimum prescription. Moreover, some patients, such as a very ill or a very young patient, might not be capable of articulating the quality of vision the various lenses afford the patient.
Objective methods of determining the patient""s refraction errors have been proposed, but these other methods introduce further complications that are not present when using phoropters. In a retinoscopy method, for example, a streak of light is projected to a patient""s retina, and the characteristics of the reflected light at the patient""s corneal plane is analyzed to determine whether the patient is myopic, or hyperopic, and with or without astigmatism. However, the method does not provide sufficient accuracy for prescribing spectacle lenses. Consequently, its measurement results are typically used only as a starting point of a standard phoropter measurement.
Another objective measurement instrument for determining refractive errors is an autorefractor, which, owing to its speed of use, is more popular than retinoscopy. To use the autorefractor, a patient is asked to look inside an enclosed box that is part of the autorefractor. A target image is optically projected into patient""s eye, and a series of lenses is automatically moved into position of the patient""s line of sight to the target, to neutralize the patient""s refractive errors (autorefraction). Unfortunately, the measurement outcome often differs from the patient""s ideal prescription. Accordingly, like retinoscopy, autorefractor outcomes typically are used only as starting points for standard phoropter measurements.
Moreover, both retinoscopy and autorefraction fail to account for the accommodation effect of the patient, that is, for the propensity of a patient to alter his or her focus or sight to make the best of the vision test. An autorefractor measurement essentially is a snapshot of the patient""s vision at a particular instant at which the autorefractor has identified a so-called neutralization point, and at this point if it happens that the patient focuses his vision for seeing an image at a distance other than what is intended, or if the patient is momentarily looking elsewhere other than the target, the output of the autorefractor is erroneous. Such deceptive focussing on the part of the patient can arise because the patient is conscious of the working distance inside the box, and when an image of an object presented to the patient which is modelled to be located at, e.g., twenty feet, the patient automatically focusses for an image at a much closer distance, knowing the actual size of the box. Examination results that include patient accommodation effects are inaccurate for prescribing spectacle lenses.
Another limitation of the autorefractor is that the examiner has no control over which lens is to be used in test. The result is that repeated measurements are likely to provide different results for the same eye from the same patient, which results in laborious and time consuming tests and retests when using the device to finalize a prescription. The present invention, having made the above-noted critical observations, provides the solutions disclosed herein.
A phoropter includes plural test lenses that can be disposed into a line of sight defined between a patient and a target, such that a patient looking at the target perceives light from the lens. A wavefront measurement apparatus is positioned to detect aberrations in light returning from the patient. The aberrations are caused by the eye of the patient.
In a preferred embodiment, the wavefront measurement apparatus includes a light source, such as a laser, for generating the light and a light detector that outputs a signal representative of the aberrations. Also, the apparatus includes a processor that receives the signal from the light detector and outputs a diagnostic signal representative thereof. The diagnostic signal is useful for generating an image representative of the test object, and/or for generating at least one visual display representative of an effectiveness of the lens in correcting a patient""s vision. The visual display can include a bar chart, a pie chart, and/or a line chart, and it can be color coded.
In another aspect, a method for indicating the quality of a patient""s vision includes providing a device through which a patient can look at a target. The method also includes directing a laser beam into the eye of a patient when the patient looks at the target, and then detecting aberrations in a wavefront of the light beam as the light beam returns from the patient""s eye. Based on the wavefront, the method indicates a quality of a patient""s vision.
In still another aspect, a method for indicating the quality of a patient""s vision includes providing a device into which a patient can look, and that generates an instantaneous visual indication of a quality of a patient""s vision.
In yet another aspect, a device for aiding a practitioner in knowing the integrated effect of a patient""s eye and a test lens placed in front of the eye includes means for sensing a wavefront of light returning from the eye through the lens. Means are coupled to the wavefront sensing means for generating an indication of the integrated effect of the eye and the test lens.
In another aspect, a device for generating an indication of the quality of vision of a patient viewing a target includes a light beam generator directing light into the eye of the patient, and a wavefront sensing device detecting the wavefront in light returned from the eye of the patient while the patient is looking at the target. A computing device receives input from the wavefront sensing device that is representative of the wavefront. The computing device outputs a continuous update of at least one of: a point spread function, and a modular transfer function, while the patient is looking at the target. A display device displays at least one of: a simulated image of the target at the patient""s retina, a quality of vision indicator indicating the quality of vision, and a graph indicating a contrast function of the patient, based at least in part on at least one of the point spread function and the modular transfer function.
In yet another aspect, a vision quantifying device includes a beamsplitter through which a patient can look at a target. A source of light emits light into an eye of the patient, which reflects from the eye as a return beam. A processor receives a signal representative of a wavefront of the return beam and generates at least one signal in response thereto, and a display receives the signal and presents a visual indication of the patient""s sight.
Another aspect of the device is to provide automatic refraction process. The patient looks at a target, a test lens is positioned between the target and the patient""s eye, and in the line of sight of the patient. A light beam is directed through the test lens and into the patient""s eye. Using a portion of that light reflected from the surfaces within the eye a wavefront profile is reconstructed. From the reconstructed wavefront profile, A quality vision factor (xe2x80x9cQVFxe2x80x9d) may be calculated. In order to improve the accuracy of the measurements of the patient""s eye, a number of measurements of the returning wavefront profile are taken, and the corresponding QVF values for each of the measurements for that particular test lens, is analyzed. The analysis of this data provides for a determination that the correction with that particular lens is optimal. If the correction is not optimal, a next test lens is selected, and the process is then repeated the next test lens after it is positioned by mechanical means in the patient""s line of sight. On the other hand, if the correction with that particular lens is optimal, than the process ends and resulting in the proper refractive correction having been identified.
The details of the present invention, both as to its structure and operation, can best be understood in reference to the accompanying drawings, in which like reference numerals refer to like parts, and in which: